Gas turbine power plants

ABSTRACT

A gas turbine power plant comprising a compressor, a turbine and a system for transmitting the drive from the turbine to the compressor, wherein the transmission system comprises at least one homopolar electrical machine connected to the turbine and operating as generator, and at least one homopolar electrical machine connected to the compressor and operating as motor, wherein this motor is supplied with electrical current from the said generator.

I Un1ted States Patent [151 3,705,775 Rioux 1 Dec. 12, 1972 [54] GASTURBINE POWER PLANTS H I Re ferencesQitetl [72] Inventor: Christian PaulGilbert Rioux, An- UNITED STATES PATENTS tony, France 2,914,688 11/1959Matthews ..310/178 [7 Assigneer Swete Natwnale d Etude et 3,585,3986/1971 Harvey ..310/178 x struction de Moteurs dAviation, Paris, FranceFOREIGN PATENTS OR APPLICATIONS 1221 Filed: Jan. 14, 1971 595,35712/1947 Great Britain ..60/269 [2] 1 Appl' 10638.0 PrimaryExaminerRobert M. Walker Attorney-William J. Daniel [30] ForeignApplication Priority Data [57] ABSTRACT Jan. 15, 1970 France ..7001437 1A gas turbine power plant comprising a compressor, a [52] U.S. Cl...417/411, 417/423, 60/269, in n a System for transmitting the drivefrom 310/178, 417/408 the turbine to the compressor, wherein thetransmis- [51] I t, Cl ..F04b 17/00, F041 35/04, F02k 3/00, sion systemcomprises at least one homopolar electri- F16 35/00 cal machineconnected to the turbine and operating as [58] Field of Search..417/408, 411, 423; 310/178; g n rat r, and at least one homopolarelectrical 318/253; 60/268, 269 machine connected to the compressor andoperating as motor, wherein this motor is supplied with electricalcurrent from the said generator.

ZQ QIaims, 15 Drawing Figures Mimi/111M 1 1 15 PATENTEU DEC 12 I972SHEET 1 BF 8 PATENTEUnEc12 I972 SHEET l [1F 8 FIGS PATENTEDUEE 12 I9723305. 775

SHEET 5 BF 8 FIG. 3

PATENTED DEC 12 I972 SHEEI 8 [IF 8 GAS TURBINE POWER PLANTS Theinvention relates generally to gas turbine power plants, and moreparticularly to power plants intended to be used as-jet propulsion powerunits in aircraft.

Gas turbine power plants used at present comprise at least onecompressor supplying one or several combustion chambers, and at leastone turbine in which the gases leaving the chamber or chambers are atleast partially expanded. The turbine supplies the power required fordriving the compressor and the auxiliary elements. Certain power plantshave different gas or air paths which may be associated with at leastone addi tional compressor or blower (multiple flow or by-passinstallations). In the following the term compressor comprises also ablower of this kind.

Up to the present it has always been the case that at least one rotarytransmission shaft has been used for connecting the turbine with thecompressor (or blower) the shaft forms an element which is simple andlight and the transmission performance of which may be very high.

However, the use of such a transmission means presents certain drawbackswhich may be particularly undesirable, particularly in power, plantswhich are required to operate under widely varying operating conditionsand from which high performances are required The speed and thedirection of rotation of the compressor are obviously determined bythose of the turbine, which makes it difficult to select the optimumspeed of the different stages of the compressor for each runningcondition. The drawbacks of this condition have been limited to someextent by-using a compressor with several stages, each of which isdriven separately by a turbine element; However, this method requiresthe use of several coaxial shafts which are very difficult to realize,since they present serious mechanical problems (great torsionalstresses, different inherent frequencies), and necessitate particularlycomplicated bearing systems.

Since successive wheels of the compressor are mechanicallyinterconnected with each other, it is necessary to provide between themfixed guide wheels which substantially increase the mass and thedimensions of the unit. It is known to eliminate this drawback bydriving two successive wheels of the compressor by a center shaft and atubular outer shaft respectively, which are connected to twocontrarotating elements of the turbine. However, the construction ofsuch a system brings about difficulties similar to thosealreadymentioned above.

The invention has the object of removing at least the major part of thedrawbacks of this transmission system, and even to remove them almosttotally in certain preferred embodiments, although these are by no meansexclusive. To this end, the invention proposes a gas turbine power plantof a kind comprising a compressor, a turbine and a system for drivingthis compressor from the turbine, wherein this driving system comprisesatleast one homopolar electric generator connected to the turbine, andat least one homopolar motor connected to the compressor and supplied bythis generator.

ln order to explain better the advantages resulting from thesearrangements, it will be necessary first to discuss some of the featuresrelating to homopolar machines, generators, or motors.

The most conventional example of a homopolar machineis the device knownas Barlow s wheel.

Like the majority of reversable electrical machines, homopolar machinesuse the interaction between an electric current and a magnetic field,the so-called induction field. The current fiows in a rotary armatureformed by an assembly of conductors'which may be separate from eachother or not. This armature has no windings or pole pieces and may haveabout its axis of rotation a strictly revolutionary symmetrical shape,becoming thereby a very simple, very light and particularly robustelement since the mechanical stresses may be uniformly distributed. Theinduction field necessary for the operation of such a machine haspreferably a revolutional symmetry. Constructions of this kind can beobtained particularly simply in the known art.

The electrodynamic force relative to theaxis of rotation is greatestwhen at each point of the armature the vector density of the current andthe magnetic field vector are perpendicular to each other and arelocated in one and the same axial plane. These conductions leave muchchoice for the construction of an efficient armature. l-lowever, amongstall the possible shapes it is possible to distinguish between twoextreme types a. homopolar machines with radial field the current linesmust be axial, and the armature may have the shape of a thin cylindricalring, the two lateral ends of which form the electrical turbines b.homopolar machines with axial field in this case the current linesmustbe radial and the armature may be formed by a thin homogenous discin which the two electrical terminals are formed by' the two concentriccircles defining the same.

Generally, the electromotive force (or counter elec- 'tromotive force) Eof a homopolar machine is given by the relation in which is the flux ofthe magnetic induction passing through the armature and m is the angularvelocity of the armature.

The utilization of homopolar machines for the transmission of energybetween the turbine and the compressor of a gas .turbine power plant isof great interest in view of their extremely high mass power, theirgreat simplicity, and their symmetry of revolution which makes themeasily integrated into the structure of the power plant, to which theyimpart a great operational flexibility, as will be shown further below.

Amongst the characteristics of homopolar machines there are certainfeatures which make the use of nonconventional means highly preferable,although not absolu tely essential for carrying out the invention, whichmeans particularly facilitate the use of highintensities and inductionfields for obtaining motors or generators which combine great powerwithan excellant electric power yield, whilst the dimensions, eitheraxial or radial, are of the same order as rotating elements inconventional gas turbine power plants.

Thus, for example, the intensity of the current flowing through thearmature of a homopolar motor driving a bladed rotor of the compressorof a gas turbine jet must be of the order of 10 to 10 amperes. At therotationalspecds which are currently used and which are comparativelyhigh, the problem of making electrical contact between the rotatingarmature and the supply leads has not been satisfactorily solved by theuse of a conventional ring type commutator, which gives rise tocomparatively high losses caused by friction and by the Joule effect. Apreferred solution consists in using a ring of liquid metal retainedbetween two conducting walls, one of which forms the fixed part, and theother the revolving part of the electric contact zone. To this end, itis possible to use, for example, mercury, a mercury-indium alloy, aeutectic of potassium and sodium, or generally any metal or alloy whichcombines good electric conductivity with a melting point which is lowerthan the temperature under which this metal or this alloy operate duringthe running of the machine, or preferably to the minimum ambienttemperature under service conditions.

The requirements relating to the electric power yield and to the powerto be transmitted lead, at the given rotational speed, to the use ofhigh flux values dz. In order to concentrate the latter within a smallregion and to reduce thereby the dimensions of the armature as far aspossible, it is necessary to utilize high intensity induction fields, ofthe order of several Teslas, which may be supplied by the coils ofsuperconducting fields.

By means of induction windings formed, for example, form an alloy ofniobium and titanium and held in a state of superconductivity by a bathof liquid helium, fields of 8 to 9 Teslas may be obtained. Alloys ofniobium and tin which are studied at present make it possible to reachvalues in excess of Teslas.

The superconducting field coils may be formed by a thin ring formed bytight turns centered on the axis of rotation of the homopolar machine.In a machine with radial field, the field may be produced by two of suchcoils located on either side of the cylindrical armature, and carryingcurrent in opposite directions. In a machine with axial field,thearrangement of the coils may be the same, but the currents must flowthrough the coils in the same direction.

The electrical consumption of superconducting field coilsin negligiblein fact, it is reduced to the dissipation under the Joule effect in theparts of the induction circuit which are not in the superconductingstate, that is to say in the connections.

Tl-le control of the speed to of a homopolar motor may be effected byacting on the intensity of the current which flows through the fieldcoil in order to modify the flux dz: if several homopolar motors areused of which each drives an element or a stage of the compressor, it ispossible to adapt the speed of each motor for any running condition ofthe power plant in such a manner that the aerodynamic yield of the unitis at optimum value. Since the current intensities flowing through thefield coils may have comparatively low values, the construction of themeans for adjusting or controlling. these values do not present anymajor technical problem. I

The particular properties of the means hereinbefore described make italso possible to solve by simple means the problems of compensationaerodynamic stresses, and of eliminating conventional bearings hithertoused for this purpose.

. from these stresses. It follows therefrom that it is possible tocalculate the armature of a homopolar machine in such a manner that theinclination of the current lines (which plays here a role rather similarto that of the blades of a wheel) gives rise to-an exact compensation ofthe resultant of the axial aerodynamic stresses affecting a wheel or agroup of combined wheels of this armature in consequence of theresultant of the corresponding axial electrodynamic stresses for anypermanent running condition. Complementary means using this principlewill be described further below and are adapted to maintain this balanceduring transitional running conditions, if necessary. By way of example,an embodiment of the invention uses for this purpose oblique slots inthe armature of machines with radial fields. I e

In so far as the radial stresses are concerned, which affect the wheels,their rotating contact of liquid metal may combine the function ofelectric conduction with that of centering bearings, using techniquesknown I from fluid hydrostatic or hydrodynamic bearings.

By way of example, we may mention the following numerical data whichcorrespond substantially to the characteristics to be looked for in adrive motor for an axial compressor with several stages in aturboreactor with fairly high thrust Total power input 1 MW Overal yield98,9 Electromotive force 20 volt Rotational speed 1,000 r.p.s. Meaninduction field: l0 Teslas The armature is of copper alloy and liquidcontacts of mercury are used. The overall output takes into account thelosses under the Joule effect in the armature and in the contacts, andthe losses incurred by viscous friction at the level of the contacts,

For the two particular types of homopolar machines referred to above,the following features are arrived at which give an idea of the factorsaccording to which a choice may be made between these two types, or atype of intermediate construction at different levels where its use mayseem desirable a. for a radial induction machine The working part of thearmature is a cylinder of mm radium, 1 mm thickness, and 50 mm length.Its mass is 280 grammes and its mass power is 4.10 W/kg.

b. For an axial induction machine The armature comprises a disc with 100mm inner radius, l20 mm outer radius, and 3 mm thickness. its mass is370 grammes and its mass power 2.7 X 10 W/kg.

Thus, in addition to their extremely high mass power, their greatsimplicity and their symmetry of revolution, which make it particularlyeasy to construct compact assemblies in a simple manner in which ahomopolar machine is perfectly integrated with an element for a stage ofa compressor or turbine without substantially increasing the mass or thebulk of these parts, the homopolar machines of an electricaltransmission in accordance with the invention may form with the currentleads which interconnect them, and the means for producing magneticinduction fields, an assembly which has generally an almost perfectrotational symmetry, which coincides very advantageously, especiallyboth in the functional plane and in the morphological plane, .with theaxial rotational symmetry which is so important to the conception andoperation of turbine power plants.

Another property of the assembly of great interest is that the mostadvantageous aerodynamic configuration in which all the stages of thecompressor and all the stages of the turbine are relativelycontra-rotating, may correspond to the simplest and most efficientelectrical layout, in which the generators and motors are in series,thereby increasing to a maximum simultaneously the mechanical,electrical and aerodynamic efiiciency, whilst maintaining the capabilityof controlling the speed of each stage in a practically independentmanner by acting independently on the current flowing through the fieldcoils, co-operating with each wheel or group of wheels.

The invention also comprises other arrangements which may be usedadvantageously in with those mentioned above in a general manner, butmay also be applied independently.

The following description given by way of example,

with reference to the accompanying drawings, explains how the inventionmay be carried into practice.

In the drawings FIG. 1 shows diagrammatically a single flow gas turbinepower plant, using an electrical transmission in accordance with theinvention, and shown in axial crosssection FIGS. 2 and 3 are axialcross-sections showing in greater detail respectively a part of thecompressor and of the turbine, forming part of the power plant shown inFIG. I

FIG. 4 is a cross-section along the line IV-IV in FIG. 2 or in FIG. 3 ofthe center structure of the power plant shown in FIG. 1

FIGS. 5 and 6 are diagrams showing in development the preferred meansfor compensating aerodynamic axial stresses FIG. 7 showsdiagrammatically in elevation a modification of the arrangements inaccordance with FIGS. 5 and 6 FIGS. 8 and 9 represent, in axialcross-section and in development, respectively, other arrangements forcompensating axial stresses, and comprising means for controlling thiscompensation;

FIGS. 10 and II represent, respectively, in elevation and in axialcross-section, a modification of the arrangements in accordance withFIGS. 8 and 9 FIG. 12 is an axial half-section of another modificationof a compressor and the means for driving the same FIG. 13 is an axialhalf-section of yet another modification of a compressor and the meansfor driving the same FIG. 14 shows diagrammatically in axialcross-section a double flow gas turbine power plant, comprising a blowerdriven by an electrical transmission according to the invention FIG. 15is a more detailed axial cross-section of the transmission elementsdriving the blower shown in FIG. 14.

The gas turbine power plant shown in FIG. 1 is of the single flow typeand is formed by a gas turbine jet engine mounted, as known per se, in ahousing 8 provided with an air inlet 9 and terminating in a jet pipe 10.Viewed in the direction of flow, this engine comprises a compressor A,for example with ten stages, a combustion chamber C, and a two-stageturbine D. The direction of the gas flow is indicated by the arrow F.Contrary to conventional arrangements, the center structure of theengine, shown generally at S, is formed by coaxial elements which areall stationary. These elements serve as supports for the rotating partsof the compressor and of the turbine, ensure the mechanical rigidity ofthe assembly, and the transmission of the electrical current produced bythe generators to the motors the path of the electrical current isindicated diagrammatically by arrows I. The center structure S isrigidly connected with the housing 8 by radial arms, such as 13 and 15.The compressor wheels A which are all contra-rotating, are drivenindependently from each other by homopolar electrical motors supplied byequally independent homopolar generators, coupled with the wheels of theturbine D which are also contrarotating. The center structure S (FIGS.2, 3 and 4) is constituted by three fixed coaxial parts a solid shaft11, and intermediate staged cylinder 16, and an outer cylinder 44. Thecenter shaft 11 forms a first electrical conductor which connects thegenerators with the motors. The intermediate cylinder 16 is keyedcoaxially to the center shaft 11 by an annular spacer 12, and a ferrule14 (FIGS. 2 and 3) which locate the shaft 11 at its ends. It forms bymeans of bearings the support for the rotor wheels of the compressor andof the turbine. The cylinder 44 is adjacent to the preceding to which itis connected. It forms a second electrical conductor between thegenerators and the motors.

The intermediate cylinder 16 which makes mechanical contact with variouselements which it supports and which have different electricalpotentials, is coated along its periphery with a coating of alumina 89(FIG. 4) which provides the necessary electrical insulation. Since thevoltage differences are always less than a few hundred volts at themost, this layer may be sufficiently thin to present no mechanicalproblem, and no impairment of the evacuation of heat. As will be seenfurther below, the center structure may be cooled by a system ofchannels in which the fuel circulates.

The compressor A, whose upstream and downstream parts are shown in FIG.2, comprises ten contra-rotating stages which are each associated withan homopolar motor.

The wheel 122 which forms the first stage of the compressor comprises aring of vanes mounted on a support consisting of a rim 124 adapted toreceive the vanes, connected by fittings 126 to the armature 128 in theform of the drum of the corresponding homopolar motor. The electriccurrent flows through the armature 12% in the axial direction. It issupplied by two rotating contacts 130 and 131 of liquid metal, locatedsubstantially at the lateral ends of the armature 128. These rotatingcontacts also form fluid bearings for centering the wheel. Each of themconsists of a ring of liquid metal wetting two co-operating surfaces,one of which forms one end of the rotating armature with which the wheel122 is firmly connected, and the other is a stationary shoulder whichsimultaneously ensures the flow of the 'cur rent and the correctposition of the wheel during rotation. r

The fixedpart of the contact 130 is a shoulder 16a of the front 'end ofthe intermediate cylinder'l6, which is in electrical contact with theconducting center'shaft 11, through theannular spacing element 12. Thefixed part of the contact 131 is a shoulder 1340 of the ring 134, whichis electrically insulated from its support 16 by the alumina film 89mentioned above.

The armature 128 may be, for example, of alloyed copper having at thesame time an excellent electrically conductivity and a satisfactorymechanical stability.

The induction field is provided by two super-com ducting fields coils 36aNd 136 comprising a certain number of turns and wound along the axis ofthe wheel. They are located substantially to the right of either end ofthe armature .128, and are supplied by current passing through each ofthem in opposite directions, so

as to provide an induction indicated schematically by the force lines(arrows B), the direction of which is substantially radial in thevicinity of the armature 128.

The following stages of the compressor have a construction identical tothe first stage, and for this reason FIG. 2 shows only the three firstand the two last stages. The rotating contacts 230 and 231 of the wheel222 of the second stage have, respectively, as fixed parts, a secondshoulder 134b of the ring 134 and a first shoulder 234a of the ring 234which, as above, is integral with the intermediate cylinder 16 andelectrically insulated against the same. The ring 134 therefore, makeselectrical contact between the downstream end of the armature 128 of thefirst stage and the upstream end'of the armature 228 of the secondstage. Similarly, in so far as the armature 228 and 328 of the secondand third stages are concerned, and so on up to the tenth stagewhichrests through the liquid contact 1031 on the shoulder 44a of the outercylinder 44, forming as outlined above, .the second element of theassembly of two conductors transmits to the compressor the electricenergy produced by the generators coupled to the turbine.

The induction field of the'homopolar motor of the second stage of thecompressor is formed by the field coil 136 and a field coil 236. Thelatter coil carries the current in the same direction as the coil 36,and the field lines, represented by the arrows B, are substan-, tiallyradial in the vicinity of the armature 228.

Theinterrnediate coils, such as for example the coil 136, are common totwo consecutive compressor stages by means of the formation of theinduction field. They are supplied in such a manner that anytwoconsecutive coils carry current in opposite directions. The feed circuitfor these coils has not been shown, but the means for its constructionwill be outlined further below.

During operation the armatures carry electric current in series and inthe same direction and have a magnetic induction flux, the sign of whichchanges from one stage to the next. It follows therefrom that any twoconsecutive stages revolve in opposite directions. It may be noted thatthis effect is obtained by the simplest possible arrangement, both ofthe armatures and of the field coils.

The field coils 36, 136T". 103 a... formed by assembly of coils ismounted in a thermal insulating casing 45 equipped with channels 46 and48 forming an inlet and an outlet for liquid helium; this casing isfitted between the center'shaft and the intermediate cylinder The fieldcoils of each homopolar motor of the compressor are preferably connectedto a general programming system, not shown, which, by manual orpreferably automatic control of the current intensity passing througheach coil, makes it possible to vary the corresponding induction fieldand to adjust the rotational speed of each stage of the compressor insuch a manner that its aerodynamic output has an optimum value under allflying conditions. Althoughthe means for obtaining the induction fieldforjeach stage are not completely independent from one stage to thefollowing, such an adjustment is practically possible within much widerlimits than thosewhich' are necessary to permit the aerodynamicadaptation mentioned above.

In the same wayas with the compressor, the stages of the turbine shownin FIG. 3 are contrarotating and each associated with the armature ofahomopolar machine. They also comprise turning contacts of liquid metalforming at the same time fluid centering bearings.

The first wheel of the turbine 1 comprises a ring of vanes mounted in arim 152 which forms part of the armature 154 of the homopolar generatorwith which it is associated. The armature.154 comprises a drum-shapedzone 154a which extends radially towards the periphery to form adisc-shaped section 154b. The arrangement of the armature 254 of thesecond stage is symmetrical to that of the armature 154, and itsconstruction is identical thereto.

The axial end of the zone 1540 makes electrical contact with a shoulder44b of the outer cylinder 44 by means of a rotating contact 161- ofliquid metal. The radial end on the periphery'of the zone 1541; makes Ielectrical contact with the corresponding part of the armature 254 bymeans of rotating contacts 162 and 262 of liquid metal through a fixedring 56 forming part of a disc 54 which is mounted on the intermediatecylinder 16. 1 Finally, a rotating contact 261 of liquid metal makeselectrical contact between the axial end of the zone 254a, having theform of the armature drum 254 and the center shaft 11 through a ferrule14. The two generators are, therefore, connected in series andelectrically connected to the motors of the compressor by the saidconductors 11 and 44. The direction of the induction fields, explainedfurther below, is such that the electromotive forces of the generatorsare additive.

The field coils of the generators, indicated by reference numerals 60,160, 260, 154, 254 are mounted substantially symmetrically relative tothe median plane of two turbine stages. The coils 60, and 260 aresupplied with current flowing in the same direction, and form asubstantially axial and comparatively uniform field in the disc-shapedpart of the armatures 154 and 254 of the generators. The two coils 164and 264 carry current in the same direction and opposite to the currentflow in the coils 60, 160 and 260. In view of the presence of thepreceding, these coils form a substantially radial field near thedrum-shaped zone of the armatures. The arrows B show diagrammaticallythe configuration of the field. Since the two turbine stages are counterrotating, it is clear that the electrical association of the armaturesjust described, which is the simplest possible, corresponds to theadditivity of the electromotive force.

As in the case of the compressor, the field coils, 60, 160,260, 164, 264are formed from a material which is maintained in the superconductingstate by liquid helium in shells 70 surrounding the coils. In the sameway as the armatures of the motors, the armatures of the generators aremade from a metal having good electrical conductivity and a strengthadequate to withstand mechanical stresses. As may be seen from FIG. 3,the disc-shaped part of the armatures of the generators actsmechanically after the manner of turbine discs of conventional turbojetengines and must withstand particula'rly considerable centrifugalstresses. For this reason, this zone may consist according to onemodification of a composite material formed from two parts which arebonded together, of which one is an alloy of conventional compositionand of high mechanical strength, and the other is thinner, consists of ahigh conductivity metal or alloy and acts as actual armature.

The circulation of the current between the armatures of the generatorsand the armatures of the motors is indicated by arrows I (FIGS. 2 and3).

It should be noted that the liquid-solid interfaces at the level of therotating contacts are so orientated that the magnetic field lines aresubstantially tangential thereto this arrangement makes it possible toeliminate losses caused by Foucault's currents inthe liquid metal duringrotation.

FIGS. 2 and 3 do not show the electric circuit feeding the fieldwindings of the homopolar machines. This circuit must supply at weakpower a current of comparatively high intensity (several thousandamperes) and may comprise, for example, a static electrical convertorcontrolled by semiconducting elements of the type known as thyristors,which make possible a very flexible control of the intensity of thecurrent flowing through them which makes them particularly suitable ascontrol elements for the speed of the revolving bladed wheels of thekind the application of which has been mentioned above.

The cooling of the central structure S which is particularly subject toheating by the Joule effect is accomplished by circulating the fuel ofthe turbojet engine through channels 72 and 74 provided in theintermediate cylinder 16, and in the center shaft 11. The fuel isadmitted into the channels 72 arranged as a ring (FIG. 4) in theintermediate cylinder 16, and flows back through U-shaped connections 76into channels '75 in the center shaft 11. The field circuit leads thento the injectors not shown in the drawing.

The axial stresses imposed on the compressor and turbine stages arecompensated by generating an electrodynamic force in the sense oppositeto the axial resultant of the aerodynamic stresses affecting the bladingof each stage. To this end a tangential component may be given to thedensity of the current in the armatures of the corresponding homopolarmachines, for example by providing slots such as shown in FIGS. 5 and 6or, more generally, by making the electric conductivity of at least partof the armature anisotropic. It

is also possible to use field coils which are so arranged that thatinduction field has an appreciable tangential component near thearmatures, but such an arrangement is not easy to realize.

FIG. 5 shows in development the configuration of the armatures of thecompressor shown in FIG. 2. Each armature comprises a set of narrowslots 68 which are regularly spaced apart, possibly filled with aninsulating or little conducting substance. These slots have the effectof inclining the current lines passing through the armatures 128 1028.

If C and F are, respectively, the moment and the axial resultant of theelectrodynamic forces generated by the flow of the current, it follows,independently of the current intensity passing through the armature,that wherein a is the mean inclination of the slopes relative to theaxis of rotation, and R is the radius of the armature. In the case of acompressor wheel, an inclination of the order of a few degrees makes itpossible to obtain the necessary axial balance which is maintained underall continuous running conditions, as already indicated above.

The current lines passing through the armatures are indicated by thedotted line I. Their inclination corresponds substantially with that ofthe slots. In view of the directional change of the induction field insuccessive armatures, the slots are directed alternately in onedirection and in the other.

FIG. 6 shows in development the configuration of the drum-shaped parts154a and 254a of the turbine armatures shown in FIG. 3, comprising anidentical system of regularly spaced slots 69. In view of the fact thatthe charge of each turbine rotor is much larger than that of eachcompressor rotor, and that the slots 69 occupy only a small part of theworking surface of the armatures 154i and 254, their inclination issubstantially greater than that of the slots 69 of the armatures of thecompressor. It is sufficient to adjust once and for all the ratiobetween the intensities flowing through the coils I64 and 264 and thoseflowing through the peripheral coils such as 160 for the compensation ofthe axial stresses to be ensured for any running condition. However,while acting separately on the fonner, it is possible to achieve duringoperation a fine adjustment of the compensation without changingsubstantially the torques of the generators.

FIG. 7 shows a modification of the embodiment which makes it possible toproduce an axial electrodynamic component in a disc-shaped armature. Tothis end, the armature 81 has a set of slots 82 which are regularlyspaced apart and inclined at an angle a relative to the planes passingthrough its axis of rotation. These slots take up a radially more orless extended zone in which the induction field B has an appreciableradial component B,.

If one assumes in the armature 81 a substantially circular ring with aradius r located in the zone of the slots 82, and if B, is the axialcomponent of the field B, the

106010 Ol2l since the means for producing the field B comprise only asingle winding,the ratio K is also independent of the intensity of thecurrent flowing through this winding, and, in the case of severalwindings, it depends only on the ratio of the intensities flowingthrough each wind- As above, a suitable value of the angle 11 makes itpossible to ensure for any continuous running condition the requiredaxial compensation.

In order to be able to carry out comfortably a fine adjustment of theelectrical compensation of axial stresses, the arrangements shown inFIGS. 8, 9, l and 11 may be used.

FIG. 8 shows diagrammatically two consecutive compressor rotors 22a and22b, each of which is rotatively driven by a homopolar machinecomprising an armature in the shape of a drum.

The armature 28a, forming part of the rotor 22a, is subjected to asubstantially radial magnetic field of the machine. An auxiliary coil37a is added to the coils 36a and 36b and is located substantially'inthe transverse median plane of the armature 28a.

v FIG. 9 shows the construction of the armature 28a of FIG. 8. Thisarmature comprises slots 80 in regular spacing, the mean inclinationofwhich is substantially unequal on either side of the median plane ofthe coil 37a. Preferably, this inclination is so chosen that when thecoil 37a does not carry current, the resulting axial electrodynamicforce substantially balances the axial aerodynamic stresses to which therotor 22a is exposed under continuous running conditions. The fieldgenerated by the How of a current in the coil 37a has the effect ofmodifying the distribution of the magnetic flux on either side of itsplane which causes a variation of the resultant of the axialelectrodynamic forces without giving rise to any appreciable variationof the overall magnetic flux of the armature, owing to the substantiallymedian position of the coil 37a relative to the armature 38a. Such anarrangement makes possible the fine adjustment of the axial force,achieving the compensation without changing the torque of the homopolarmachine. This application is particularly suitable for producing astrict axial compensation, particularly during the transitional runningconditions of a turbo machine in accordance with the invention.

The homopolar machine driving the rotor 22b shown in FIG. 8 has similararrangements. Obviously, taking into account the respective directionsof the field and of the current flow, the orientation of the slots inthe armature 38b must be symmetrical to that of the slots of thearmature 28a.

The arrangement shown in FIGS. 10 and 11 relates to a homopolar machinewith axial field, and has the same object as that shown in FIGS. 8 and9.

The armature 83 in the shape of a disc has slots 84 inclined relative toits axial planes, and the shape of which depends only on the mostdesirable radial distribution of the axial electrodynamic forces whichthey generate. Two identical coils 85 and 86, the diameters of which arepreferably similar to the outer diameter of the armature 83, are mountedcoaxially in two planes symmetrical relative thereto. They carrycurrents in the same direction which create a magnetic field, thedirection of which is substantially axial in the zone of the armature83, and the control of which makes it possible to vary the moment takenup or supplied by the machine. The auxiliary coils 87 and 88, arrangedinthe same manner as described above and having a diameter preferably nearthe inner diameter of the armature 83, carry currents in the oppositedirection. The axial and radial components of the magnetic field formedby each of them in the zone of the armature 83 are, respectively,subtractive and additive, with the result that if the coils carrycurrents of the same intensities, the magnetic flux of the armature isindependent therefrom and the control of this intensity modifies onlythe radial component of the field, that is tosay the electrodynamiccompensating force of the axial stresses.

FIG. 12 shows in axial cross-section an embodiment of the inventionsuitable for driving the rotor ofa compressor element with rotor andstator. This element comprises, as known in the art, a row of fixedbladed rings, such as 11 18 forming part of a housing 1000, andalternating with a row of rotating vane rings, such as 1 119, mounted ona drum 1 which turns in bearings 1121 and 1122. V

The drum 1120 is rotatively driven by a homopolar electric motor formedby a set of alternatively fixed and rotating discs, such as 1123 and1124, respectively, and a field coil 1125 retained by a ringv 1126forming part of the ring 1131 of a fixed vane ring 1118.

a The set of rotating discs 1124 forms the actual armature of thehomopolar motor these discs are fixed with their outer edges on the drum1120, but are electrically insulated against the same. The fixed 'discs.1123, located between the rotating discs 1124, make electrical contactbetween the outer edges of such fixed rotating discs and the inner edgesof the adjacent rotating discs, by means of revolving contacts such asl127' which are preferably formed by a'ring of liquid metal. Finally,the outermost discs 1123a and 1124a make electrical contact withconducting cylinders 1128 and 1129 respectively, between which ismounted an insulating cylindricalsleeve 1130, on which are fixed thestationary discs other than 1123a. 7 I

The field coil shown diagrammatically at 1125 is formed by asuperconducting winding surrounded by a cryogenic element. This windinghas turns coaxial with the armature. The arrow B shows the lines of themagnetic field generated by the coil 1125. In the zone occupied by thediscs 1124, the field B is substantially homogenous and axial. Thearrows I shown the current path across thearmature it may be seen thatit passes each disc 1124 in the same direction. It follows therefromthat the Laplace forces caused by the field B and by the current Igenerate in each disc 1124 electrodynamic moments in the same direction.

The motor is connected to the associated homopolar generator, not shown,by means of a cylindrical conductor 1 129 and a center conductor 1 1 11.

FIG. 13 shows a modification of the counter rotating compressorillustrated in FIG. 2, in which, however, the arrnatures are notcylindrical but disc-shaped.

This compressor may comprise, for example, eight contra-rotating bladerings 1219 which rest during rotation, through means described furtherbelow, on a hollow cylinder 1211 which is fixed and servessimultaneously as electrical conductor and as frame for the compressorassembly. The cylinder 1211 may be fixed, for example, by means ofradial arms (not shown) to a housing (not shown) which defines in aconventional manner the flow of gas at the periphery of the blading.

Each stage of the compressor comprises a ring of vanes 1219 fixed to arim 1231 forming part of a disc 1224 which forms the armature of theassociated homopolar motor. On either side of each armature 1224 andcoaxially relative thereto are mounted superconducting windings 1125surrounded by a cryogenic shell 1125a, containing circulatingliquidhelium and mounted on fixed elements, such as discs, indicated at 1223,1223a, 1223b, which are'mechanically integral with the cylindricalsupport 1221 and electrically insulated against the same by a layer ofalumina (not shown).

The windings 1225 carry current in the same direction and generate anaxial magnetic field whose lines of force are diagrammatically indicatedby arrows B.

With the exception of the first upstream blade ring, the inner edge ofthe armatures 1224 forms a first electrical terminal which rests on oneof the lateral ends of a cylindrical foot 1228 of the fixed discs 1223aby means of a rotating contact 1227a of liquid metal. The armatures1224' have at their periphery a circular shoulder 1224a forming a secondelectrical terminal which rests through another rotating electricalcontact 1227b of liquid metal on a conducting bush forming part of thefixed discs 1223b which alternate in the axial direction with the fixeddiscs 1223a.

In the upper part of the zonelocated between two consecutive windings1225, the field B has an appreciable radial component. The orientationof the armatures 1224 therefore evolves and has an inclined portion1224b in the corresponding zone. It may also be noted that the meridiancontour of the surfaces defining the rotating contacts 1227a and 1227b:is substantially parallel to the lines of the field B in theirvicinity. In this manner, it may be avoided that during the rotationparasitic currents appear in the liquid metal which might lead tosubstantial losses.

It may also be seen from FIG. 13 that the general arrangement of thearmatures is such that the assembly formed by two consecutive contactsis generally symmetrical in relation to the median plane of the fixeddisc 1223a or 1223b (as the case may be) mounted between thesearmatures. It may be noted that the arrangement of the first and of thelast stage of the com pressor differs from that of the intermediatestages, in that the rotating contact 1227a of the first stage is indirect contact with the center cylinder 1211, and the cylindrical foot1228' of the last fixed disc 1223a is formed by an extension of theannular conductor 1212 which surrounds the conductor 1211. As in thepreceding cases, the conductors 1211 and 1212 are connected to thehomopolar generator, not shown.

The arrows I in FIG. 13 indicate diagrammatically the path of the feedcurrent of the armatures 1224. It may be seen that the elements 1228 and1229 mount the'assembly of armatures electrically in series, and thattwo consecutive armatures carry currents flowing in opposite directionsand generally axial magnetic fields in the same direction. It followstherefrom that the Laplace forces moments acting on each of them haveopposite signs, as also the directions of the rotation of consecutiveblade rings 1219a and 1219b driven by them, as described hereinbefore.

The radial and axial stresses of each stage of the compressor duringrotation are contained according to two separate systems. The radialstresses are absorbed by the rotating contacts of liquid metal, whichfulfil the function of liquid centering bearings. With a view tocarrying out the compensation of axial stresses, the armatures 1224shown in FIG. 13 have, as indicated above with reference to FIG. 7,inclined slots 12240 which are uniformly distributed. over theircircumference in a zone in which the field B has a noticeable radialcomponent. The inclination of these slots makes it possible to give thedensity vector of the current a tangential component which isporportional to the generated electrodynamic force. The direction of theinclination of the slots 1224c corresponds to the compensation of theaxial aerodynamic stresses, the direction of the current I flowingthrough the armature, and the direction of the magnetic field beingassumed to be as shown in FIG. 13.

For an observer located on the same side of the compressor blades shownin FIG. 13, the direction of the slope of the the slots 1224c is thesame for the armatures of rotating blade rings 12190 which rotate in onedirection, and 1219b rotating in the other direction.

The driving installation of a double flow gas turbine showndiagrammatically in FIG. 14 comprises, as

' known in the art, a front fan 10 of high dilution rate which forcesair on the one hand into an annular peripheral conduit formed between anouter casing 2c and a shell 3c, and on the other hand into a centerconduit comprising, in-the direction of flow, two compressor elements 40and 50 respectively of low and high pressure, a combustion chamber 6cand a high pressure and low pressure turbine element 7c and 8crespectively.

According to the embodiment of the invention, the transmission of energysupplied by the expanding members to the compression members is effectedby mixed means in that it comprises the use of an electricaltransmission according to the invention with conventional means. Theelements 4c and 5c of the compressor are connected in a conventionalmanner by coaxial rotating shafts 9c and 10: to the correspondingturbine elements 8c and 70, whilst the fan 1c is driven by an electricaltransmission shown diagrammatically at 110, which as will be seenfurther below in greater detail, comprises a homopolar generatorconnected to the low pressure turbine 8c through the shaft 9c andsupplying a homopolar motor which supplied the fan with the torquenecessary for its actuation.

This arrangement makes it possible to eliminate the necessity fordriving the fan by an additional low pressure turbine which,particularly if the required dilution rate is high, must turn at verylow speed, and must therefore comprise a large number of stages whichwork under particularly unfavorable conditions. The electrical homopolartransmission machines 11c may be constructed in such a way that theoptimum rotation of the fan 1c is obtained with a rotational speed ofthe shaft corresponding only to the conditions of good adaptation of thecompressor 4c and the turbine 80 of which it forms a part.

FIG. shows in greater detail an embodiment of the electric transmission11c connecting the blower to the low'pressure turbine of theturboreactor in accordance with FIG. 14.

This transmission comprises in a profiled casing 12c, coaxial to thehousing 3c (FIG. 14) and fixed thereto by means not shown, a homopolargenerator 14c and a homopolar motor 15c whose respective armatures 16cand 170 are discs with radially decreasing thickness towards theperiphery, so that the density of the current flowing therethrough issubstantially uniform.

The armature 160 is fixed through a link 18c to a tubular shaft 19cwhich fonns an extension of the rotor 200 of the low pressure compressor4c (FIG. 14) ,upstream of a ballbearing 210 in which it is mounted.

The ring of rotating vanes 1c of the blower is mounted on a. conicalelement 220 forming an extension of a tubular shaft 230 which is coaxial'with the shaft 190, comprising a flange 240 which carries the armaturel'7c of the homopolar motor 15c. The shaft 23c revolves in a ballbearing 25c and in a roller bearing 26c, the outer race of which ismounted on the shaft 190 at the point of the bearing 21c.

The bearings 21c and 25c are mounted with their outer races,respectively, to an inner extension 260 of the casing 120 and to a stay27c forming therewith a rigid structure.

A fixed annular conductor 28c integral with the stay 27c interconnectsthe radial peripheral ends of the armatures 16c and 170 by means ofrotating contacts 29c and'30c, respectively, of liquid metal. An annularconductor 31c mounted on the base of the armature 17c connects thisarmature to the base of the armature 16c by means of a third revolvingcontact 320 of liquid metal. This constitutes a closed electric circuitwhich comprises the armature 16c, the fixed conductor 28c, the armature17c, and its extension 31c. The circuit is immersed in its entirety intothe substantially axial magnetic field generated by a superconductingwinding shown diagrammatically at 33c, and mounted on the stay 27c. Inview of the configuration of the circuit, the armatures 16c and 17arevolve in the same direction and their respective speeds are in thesame ratio as the magnetic fluxes flowing through them. This ratio isdetermined by the radial heigh of the conductor 280 which acts asreaction element.

In order to make possible the use in the rotating contacts of an alloysuch as sodium-potassium eutectic, which is highly oxidizable, a tightchamber 340 comprising means (not shown) for introducing an inner gasunder pressure, such as nitrogen or argon, is formed around the electriccircuit by means of enclosures 35c and 360 fixed to the conductor 28cand provided with fittings 37c and 380 which make tight contact with theshafts 19c and 230, and a third sealing element 39c arranged between theshafts.

The wall 360 is electrically insulated against the conductor 28c andsupports the fixed element 40c of a rotating contact 2 lc, the movingpart of which consists of a flange 42c forming part of the armature 17cand electrically connected the-reto. Thus, when the installation isunder running conditions, it is possible to obtain between the wall 36cand its support 28c, an electric voltage capable of supplying, throughconductors not I shown, the different electrical installations providedon board of the aircraft. Moreover, the starting of the installation maybe achieved by connecting at a given moment the said conductors to anexternal source of electrical energy.

The bearings 21c, 25c and 260 are located on either side of the fieldwinding 33c and at a certain distance therefrom. This measure has theobject of eliminating the generation of induced currents in the rollingelements, such as balls or rollers. Moreover, andwith the same object inview, windings 43c and 44c are located in the vicinity of these bearingsand have the object of generating a magnetic field, which opposeslocally the magnetic field generated by the winding 33c. Thesearrangements are completed by shielding elements 450 and 46c, formed bya ring of high magnetic permeability which make it possible to suppressthe'effects of the residual field in the bearings 21c and 25c.

As already explained further above,the.speed ratio between the fan 1cand the rotor 200 is defined by the ratio between the magnetic fluxespassing through the armatures 16c and 170. In the arrangement of FIG. 15and in view of the uniqueness of the field windings 33c, this ratiodepends only on the geometrical layout of the armatures. However, with aview to making this ratio variable, it is possible to replace the saidwinding 33c by two distinct field windings provided with means forvarying the ratio between the current intensities passing through them.

Obviously, the embodiments hereinbefore described are given merely byway of example, and may be modified, particularly by substitutingtechnical equivalents, without thereby departing from the principle ofthe invention.

I claim: I

1. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor, and a homopolar electrical machine including(a) an armature connected to said bladed rotor for rotation therewith,said armature being traversed by an electrical current and includingmeans defining for the flowof current in said armature a path having acomponent extendingin a plane passing perpendicular to the axis of therotor, and (b) magnetic field generating means for producing at least one induction field through said armature, said induction field having acomponent extending in the same plane as and normal to said firstmentioned component, whereby there is imparted to the rotor anelectrodynamic force having a component parallel to said rotor axis.

2. A turboelectrical unit according to claim 1 wherein at least aportion of the armature of the homopolar machine has, with respect toits electrical conductivity, an anisotropic structure adapted to impartto the lines of electrical current in said armature a component directedtangentially with respect to the axis of said rotor. I

3. A turboelectrical unit according to claim 2 wherein said portion ofthe armature of the homopolar machine is formed with slots inclined awayfrom a radial plane passing through the axis of said rotor, said slotscomprising said current path defining means.

4. A turboelectrical unit according to claim 3 wherein said slots areconstituted by plural axial sections of different inclinations.

5. A turboelectrical unit according to claim 4 wherein said magneticfield generating means is adapted to produce separate induction fieldsthrough the portions of the armature carrying the respective slotsections and comprises means for varying the ratio between said separateinduction fields.

6. A turboelectrical unit according to claim 5 wherein said magneticfield generating means include at least one main field winding, and saidvarying means include at least one auxiliary field winding.

7. A turboelectrical unit comprising: an axial flow turbomachineincluding at least one bladed rotor; and at least one homopolarelectrical machine including (a) an armature rotating with said rotorand comprising a disc-like section and (b) magnetic field generatingmeans adapted to produce an induction field through said armature andcomprising two windings mounted on either side of said disc-like sectionin coaxial relation therewith, said winding being traversed byequidirectional currents. v a

8. A turboelectrical unit according to claim 7 comprising at least twoconsecutive independent bladed rotors each having a disc-like armaturesection rotating therewith, each of said disc-like sections includingtwo annular electrical terminals with different diameters coaxial withsaid rotors, said unit further comprising a fixed support carrying afixed element between and coaxial with said rotors, said fixed elementincluding an electrically conductive ring coaxial with said rotors andconnecting electrically through sliding contacts with the correspondingannular terminals on the rotors adjacent thereto.

9. A turboelectrical unit according to claim 8 wherein at least one ofthe electrical terminals on each rotor is of frustoconical shape and,through a sliding electrical contact, bears on a correspondingly shapedfrustoconical portion on said fixed element.

10. A turboelectrical unit according to claim 8 wherein said fixedelement carries a field winding.

11. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor; and at least one homopolar electrical machineincluding (a) an armature rotating with said rotor comprising asubstantially axially extending drum-like section and (b) magnetic fieldgenerating means adapted to produce an induction field through saidarmature and comprising two windings mounted in coaxial relation withsaid drum-like section and traversed by currents flowing in oppositedirections.

12. A turboelectrical unit according to claim 11 comprising at least twoconsecutive independent bladed rotors having a drum-like armaturesection rotating therewith, each such section including two annularelectrical terminals coaxial with said rotors, said unit furtherincluding a fixed support carrying a fixed element between and coaxialwith said rotors, said fixed element including an electricallyconductive ring coaxial with said rotors and connecting electricallythrough sliding contacts the corresponding annular terminals on therotors adjacent thereto.

13. A turboelectrical unit according to claim 12 wherein at least one ofthe electrical terminals on each rotor is of frustoconical shape and,through a sliding electrical contact, bears on a correspondingly shapedfrustoconical portion on said fixed element.

14. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor; and at least one homopolar electrical machineincluding (a) an armature rotating with said rotor and comprising afirst disc-like section and a second substantially axially extendingdrum-like section, (b) first magnetic field generating means adapted toproduce a substantially axial induction field through said disc-likesection and including two windings mounted on either side of saiddisc-like section and coaxial therewith, said windings being traversedby equidirectional currents, and (c) second magnetic field generatingmeans adapted to produce a substantially radial induction field throughsaid drum-like section and including at least one winding mountedcoaxial to said drum-like section for traversal by an electrical currentflowing in a direction opposite to the direction of said equidirectionalcurrents.

15. A turboelectrical unit comprising: a fixed support; an axial flowturbomachine including at least one bladed rotor rotating on saidsupport; at least one homopolar machine including an armature beingtraversed by an electrical current and including at least one rotaryannular electrical terminal coaxial with said rotor; a fixed annularelectrical terminal mounted on said fixed support in coaxial relationwith said rotary annular terminal; and bearing means for rotatablysupporting said rotor on said fixed support, said bearing meansincluding means for maintaining said rotary annular electrical terminalin sliding electrical contact with said fixed electrical terminal.

16. A turboelectrical unit according to claim 15 wherein said bearingmeans include liquid metal bearing means adapted to provide saidelectrical sliding contact.

17. A turboelectrical unit comprising: a fixed support; an axial flowturbomachine having at least one bladed rotor; bearing means formounting said rotor for rotation on said fixed support; at least onehomopolar electrical machine including (a) an armature rotating withsaid rotor, (b) main magnetic field generating means adapted to producean induction field through said armature, and (c) auxiliary magneticfield generating means adapted to produce in the region of said bearingmeans a magnetic field opposed to that produced by said main magneticfield generating means.

18. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor; at least one homopolar electrical machineincluding an armature rotating with said bladed rotor for traversal byan electrical current; an auxiliary electrical circuit, and meanselectrically connecting said armature with said auxiliary circuit.

19. A gas turbine power plant comprising:

a. an axial support,

b. a compressor rotor mounted on said support,

0. a turbine rotor mounted on the same support in axially spacedrelation to said compressor,

(1. at least one homopolar electrical machine including an armaturerotating with said turbine rotor and fixed field means cooperating withsaid armature to generate an electrical current therein upon rotationthereof,

at least one additional homopolar electrical machine including anarmature rotating with said compressor rotor and including fixed fieldmeans cooperating with said armature to rotate the same upon the passageof an electrical current therethrough, and

conductor means establishing an electrical circuit between the armaturerotating with the turbine rotor and the armature rotating with thecompressor rotor, said conductor means comprising:

1. outside fixed conductor means provided adjacent the exterior of saidaxial support in the region extending between said armatures and in theregions adjacent the remote sides of said armatures,

2. sliding contact means connecting opposite sides of the respectivearmatures with the adjacent terminations of said outside fixed conductormeans, and

3. inside fixed conductor means extending within the interior of saidaxial support and connected at its opposite ends to the outside fixedconductor means in the regions adjacent the remote sides of saidarmatures.

20. The power plant according to claim 19 wherein said outside fixedconductor means comprises an intermediate generally annular casingsection extending between the armatures, a forward generally annularcasing section upstream of the armature rotating with said compressorrotor and a rearward generally annular casing section downstream of thearmature rotating with said turbine rotor, all of said casing sectionscomprising conductive material.

1. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor, and a homopolar electrical machine including(a) an armature connected to said bladed rotor for rotation therewith,said armature being traversed by an electrical current and includingmeans defining for the flow of current in said armature a path having acomponent extending in a plane passing perpendicular to the axis of therotor, and (b) magnetic field generating means for producing at leastone induction field through said armature, said induction field having acomponent extending in the same plane as and normal to said firstmentioned component, whereby there is imparted to the rotor anelectrodynamic force having a component parallel to said rotor axis. 2.A turboelectrical unit according to claim 1 wherein at least a portionof the armature of the homopolar machine has, with respect to itselectrical conductivity, an anisotropic structure adapted to impart tothe lines of electrical current in said armature a component directedtangentially with respect to the axis of said rotor.
 2. sliding contactmeans connecting opposite sides of the respective armatures with theadjacent terminations of said outside fixed conductor means, and 3.inside fixed conductor means extending within the interior of said axialsupport and connected at its opposite ends to the outside fixedconductor means in the regions adjacent the remote sides of saidarmatures.
 3. A turboelectrical unit according to claim 2 wherein saidportion of the armature of the homopolar machine is formed with slotsinclined away from a radial plane passing through the axis of saidrotor, said slots comprising said current path defining means.
 4. Aturboelectrical unit according to claim 3 wherein said slots areconstituted by plural axial sections of different inclinations.
 5. Aturboelectrical unit according to claim 4 wherein said magnetic fieldgenerating means is adapted to produce separate induction fields throughthe portions of the armature carrying the respective slot sections andcomprises means for varying the ratio between said separate inductionfields.
 6. A turboelectrical unit according to claim 5 wherein saidmagnetic field generating means include at least one main field winding,and said varying means include at least one auxiliary field winding. 7.A turboelectrical unit comprising: an axial flow turbomachine includingat least one bladed rotor; and at least one homopolar electrical machineincluding (a) an armature rotating with said rotor and comprising adisc-like section and (b) magnetic field generating means adapted toproduce an induction field through said armature and comprising twowindings mounted on either side of said disc-like section in coaxialrelation therewith, said winding being traversed by equidirectionalcurrents.
 8. A turboelectrical unit according to claim 7 comprising atleast two consecutive independent bladed rotors each having a disc-likearmature section rotating therewith, each of said disc-like sectionsincluding two annular electrical terminals with different diameterscoaxial with said rotors, said unit further comprising a fixed supportcarrying a fixed element between and coaxial with said rotors, saidfixed element including an electrically conductive ring coaxial withsaid rotors and connecting electrically through sliding contacts withthe corresponding annular terminals on the rotors adjacent thereto.
 9. Aturboelectrical unit according to claim 8 wherein at least one of theelectrical terminals on each rotor is of frustoconical shape and,through a sliding electrical contact, bears on a correspondingly shapedfrustoconical portion on said fixed element.
 10. A turboelectrical unitaccording to claim 8 wherein said fixed element carries a field winding.11. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor; and at least one homopolar electrical machineincluding (a) an armature rotating with said rotor comprising asubstantially axially extending drum-like section and (b) magnetic fieldgenerating means adapted to produce an induction field through saidarmature and comprising two windings mounted in coaxial relation withsaid drum-like section and traversed by currents flowing in oppositedirections.
 12. A turboelectrical unit according to claim 11 comprisingat least two consecutive independent bladed rotors having a drum-likearmature section rotating therewith, each such section including twoannular electrical terminals coaxial with said rotors, said unit furtherincluding a fixed support carrying a fixed element between and coaxialwith said rotors, said fixed element including an electricallyconductive ring coaxial with said rotors and connecting electricallythrough sliding contacts the corresponding annular terminals on therotors adjacent thereto.
 13. A turboelectrical unit according to claim12 wherein at least one of the electrical terminals on each rotor is offrustoconical shape and, through a sliding electrical contact, bears ona correspondingly shaped frustoconical portion on said fixed element.14. A turboelectrical unit comprising: an axial flow turbomachine havingat least one bladed rotor; and at least one homopolar electrical machineincluding (a) an armature rotating with said rotor and comprising afirst disc-like section and a second substantially axially extendingdrum-like section, (b) first magnetic field generating means adapted toproduce a substantially axial induction field through said disc-likesection and including two windings mounted on either side of saiddisc-like section and coaxial therewith, said windings being traversedby equidirectional currents, and (c) second magnetic field generatingmeans adapted to produce a substantially radial induction field throughsaid drum-like section and including at least one winding mountedcoaxial to said drum-like section for traversal by an electrical currentflowing in a direction opposite to the direction of said equidirectionalcurrents.
 15. A turboelectrical unit comprising: a fixed support; anaxial flow turbomachine including at least one bladed rotor rotaTing onsaid support; at least one homopolar machine including an armature beingtraversed by an electrical current and including at least one rotaryannular electrical terminal coaxial with said rotor; a fixed annularelectrical terminal mounted on said fixed support in coaxial relationwith said rotary annular terminal; and bearing means for rotatablysupporting said rotor on said fixed support, said bearing meansincluding means for maintaining said rotary annular electrical terminalin sliding electrical contact with said fixed electrical terminal.
 16. Aturboelectrical unit according to claim 15 wherein said bearing meansinclude liquid metal bearing means adapted to provide said electricalsliding contact.
 17. A turboelectrical unit comprising: a fixed support;an axial flow turbomachine having at least one bladed rotor; bearingmeans for mounting said rotor for rotation on said fixed support; atleast one homopolar electrical machine including (a) an armaturerotating with said rotor, (b) main magnetic field generating meansadapted to produce an induction field through said armature, and (c)auxiliary magnetic field generating means adapted to produce in theregion of said bearing means a magnetic field opposed to that producedby said main magnetic field generating means.
 18. A turboelectrical unitcomprising: an axial flow turbomachine having at least one bladed rotor;at least one homopolar electrical machine including an armature rotatingwith said bladed rotor for traversal by an electrical current; anauxiliary electrical circuit, and means electrically connecting saidarmature with said auxiliary circuit.
 19. A gas turbine power plantcomprising: a. an axial support, b. a compressor rotor mounted on saidsupport, c. a turbine rotor mounted on the same support in axiallyspaced relation to said compressor, d. at least one homopolar electricalmachine including an armature rotating with said turbine rotor and fixedfield means cooperating with said armature to generate an electricalcurrent therein upon rotation thereof, e. at least one additionalhomopolar electrical machine including an armature rotating with saidcompressor rotor and including fixed field means cooperating with saidarmature to rotate the same upon the passage of an electrical currenttherethrough, and f. conductor means establishing an electrical circuitbetween the armature rotating with the turbine rotor and the armaturerotating with the compressor rotor, said conductor means comprising: 20.The power plant according to claim 19 wherein said outside fixedconductor means comprises an intermediate generally annular casingsection extending between the armatures, a forward generally annularcasing section upstream of the armature rotating with said compressorrotor and a rearward generally annular casing section downstream of thearmature rotating with said turbine rotor, all of said casing sectionscomprising conductive material.